The present invention relates to a switch comprising a deflectable inertial mass that responds to acceleration, by means of which a switching system can be actuated.
Such switches are needed in vehicles so that the activation of restraint systems is only triggered when a (negative) acceleration is detected that indicates a vehicle collision. Extremely high demands have to be made of the functional reliability of such a switch.
DE 195 18 824 C1 already discloses a switch of this type including an inertial mass which is guided so as to move in a guide housing and is spring-loaded to a resting position. The inertial mass is configured so as to be of revolution or spherical. The inertial mass actuates an electric contact pair which, in turn, is biassed to a resting position. In a first movement phase, the inertial mass only approaches the electric contact pair. Only when its higher restoring force, in addition to the spring that presses against the inertial mass, has been overcome is the contact made. In this manner, a reliable contact is made over a predefined time duration without contact bounces.
With other known switches, mechanical actuation systems with a snap effect or with magnetically actuated switching elements are used. All of the known solutions have in common that, in order to achieve reliable and reproducible switching behavior, they require a complex structure and/or a critical adjustment.
The present invention provides a switch that, with just a few simple components, ensures a reliable and readily reproducible switching function without any requirement for adjustment.
The switch according to the invention comprises a deflectable inertial mass that responds to acceleration, by means of which a switching system can be actuated. The inertial mass is suspended on two parallel, elastically deflectable support arms each having a first, firmly anchored end and a second, movable end to which the inertial mass is attached. The two elastically deflectable support arms form a guide parallelogram that, when the inertial mass is deflected, forces it to make an essentially parallel movement and, at the same time, it exerts a restoring force. Since the inertial mass is preferably secured between the support arms with a gap on both sides, it does not touch any other components when it is deflected, so that its movement is not hindered by any friction whatsoever.
Conventional switches to trigger the activation of restraint systems in vehicles can only respond to acceleration in one direction. Normally, they are designed for front-impact collisions. The switch according to the invention, however, makes it possible in an extremely simple manner to actuate two switching systems, one for frontal collisions and one for rear-end collisions, since the inertial mass can be deflected in two opposite directions.
Preferably, the switch is built on a baseplate in which the unmovable ends of the support arms are anchored. The inertial mass with the bearings and the switching system are enclosed by a hood-like housing that is connected to the circumferential edge of the baseplate. Contact pins are also anchored in the baseplate and they allow the direct attachment of the switch contact members onto a printed circuit board The switch can be quite compact in design. In the case of a parallelepipedal housing, the edge length can be less than 20 mm.
With the configuration of the switch according to the invention, multifaceted forms and arrangements of switching systems can be used In the simplest case, the inertial mass has an actuation arm that engages a spring contact element In this case, preferably a normally closed contact pair is used which is held in its open position by the actuation arm of the inertial mass, as long as the inertial mass is in its non-deflected resting state and, when the inertial mass is deflected, the actuation arm is retracted and the contact pair automatically assumes the closed position. Movement of the inertial mass then no longer has any influence on the switching behavior of the switching system. It only determines the status of the switching system, i.e. on or off.
When higher demands are placed on the functionality of the switch, then more complex switching systems can be used, for example, optical or magnetic switching units. Aside from the elementary switching function, these units can generate additional switching signals for various purposes, especially for signals that can also be used for diagnostic purposes.